Generally, a semiconductor device may be formed by depositing multiple layers of thin films such as a poly-silicon layer, an oxide layer, a nitride layer and/or a metallic layer on a wafer and forming a pattern thereon after a photolithography process, an etching process, a diffusion process and/or an ion implantation process.
The photolithography process is a core technology for manufacturing semiconductor devices. In the photolithography process an integrated circuit pattern may be formed on a wafer by exposing a photo mask with a micro circuit formed therein to a certain light source. Light sources that are currently used in known photolithography processes include g line, I line, Deep Ultra Violet (DUV), KrF laser, etc. Photolithography processes use a photo resist layer, which consists of photosensitive polymer whose solubility changes in response to light exposure.
When exposed to light through the photo mask, the portion of the photo resist layer which is exposed to light is changed into soluble material or insoluble material in comparison with a portion of the photo resist layer that is not exposed to light. The soluble or insoluble materials respectively form positive or negative patterns in the photo resist layer if they are developed by a developing solution. The pattern formed in the photo resist layer serves as a mask in a post-photolithography process such as, for example, an etching process or an ion implantation process, etc.
The photo resist layer is generally coated on a wafer by a conventional spin coating apparatus such as the apparatus 100 shown in FIG. 1. The spin coating apparatus 100 comprises a chuck 10 for holding a wafer 1 using vacuum suction, a vertical drive axis 20 connected to a lower portion of the chuck 10, a spin driver 30 installed on one side of the vertical rotation axis 20, a carrier arm 40 for supplying resist solution, a carrier arm 50 for top edge bead removal (TEBR), and a nozzle 60 for back side rinse (BSR). The carrier arm 40 carries a nozzle unit 41 and is installed such that it can be horizontally and vertically moved so as to inject the resist solution (which is not shown) on an upper portion of the wafer 1 through the nozzles 42 of the nozzle unit 41. The carrier arm 50 for TEBR carries a nozzle unit 51 and is installed such that it can be horizontally and vertically moved so as to downwardly inject a solution (e.g., a thinning agent such as a solvent) for TEBR, on the upper portion of the wafer 1 through the nozzle 52. Also, the nozzle 60 for BSR is installed so as to upwardly inject a solution (e.g., a thinning agent such as a solvent) for BSR to a lower portion of the wafer 1.
The spin coating apparatus 100 of FIG. 1 spin-coats a photo resist layer (which is not shown) on a wafer 1 in accordance with the process illustrated in FIG. 2. That is, when the wafer 1 is positioned on the chuck 10 and secured thereto with vacuum suction, the vertical rotation axis 20 is rotated at high speed (e.g., in the clockwise direction) by a driving force applied by the spin driver 30 (Step S11). The wafer 1 is simultaneously rotated (e.g., in clockwise direction) together with the chuck 10. In the illustrated example, the wafer 1 is vacuum-sucked onto the chuck 10 such that its upper portion, (e.g., the surface on which a semiconductor device is to be formed), faces upward.
While the wafer 1 is rotated at a constant speed, the carrier arm 40 moves the nozzle unit 41 generally horizontally forward toward the chuck 10 to position the nozzles 42 vertically above the wafer 1 and then moves the nozzle unit 41 generally vertically downward to lower the nozzles 42 to a certain level above the wafer 1. Then, a certain amount of resist solution is downwardly injected onto a center region of the upper surface of the wafer 1 through the nozzles 42 of the nozzle unit 41. (Step S13). The nozzle unit 41 is then returned to its original position by the carrier arm 40. Since the wafer 1 is rotated at high speed, centrifugal forces spread the resist solution outward from the center region of the wafer 1 to the outer edge portion of the wafer 1 to coat the entire surface of the wafer 1 so as to form a photo resist layer having a uniform thickness.
When the photo resist layer is formed, contaminants such as dregs of the photo resist layer are likely to be left on the upper edge portion and the lower portion of the wafer 1. Such contaminants should be removed so as to prevent defects during post-processing.
To this end, the carrier arm 50 for TEBR moves the nozzle unit 51 generally horizontally forward to the upper edge of the wafer 1 and then moves the nozzle unit 51 generally vertically downward to lower the nozzle 52 to a certain level above the wafer 1. Then, a certain amount of TEBR solution (e.g., a thinning agent) is downwardly injected on the edge of the wafer 1 through the nozzle 52. (Step S15). The nozzle 52 is then returned to its original position by the carrier arm 50. Also, a certain amount of BSR solution (e.g., a thinning agent) is upwardly injected onto the edge of the wafer 1 through the nozzle 60. (Step S15).
Since the wafer 1 is rotated at high speed, a uniform width (e.g., about 3 mm) of the photo resist layer on the upper edge of the wafer 1 is removed together with contaminants of the photo resist layer on the lower portion of the wafer 1. This removal is carried out in order to remove contaminants such as dregs of the photo resist layer that may have been left on the upper edge and the lower portion of the wafer 1. The thinning agents for TEBR and BSR use the same kind of thinning agent (e.g., a solvent, etc).
When the TEBR and BSR processes are terminated, the spin driver 30 stops rotating the vertical rotation axis 20. The wafer 1 then stops rotating together with the chuck 10. (Step S17) The coating process of the photo resist layer for one wafer 1 is thus terminated.
The thinning agents supplied to the nozzles 305, 306 for TEBR and BSR are supplied by a thinning agent supplying system. A conventional thinning agent supplying system is constructed as shown in FIG. 3. The system of FIG. 3 comprises an input terminal 301 for receiving and supplying thinning agent, a storage tank 302 for receiving and storing thinning agent from the input terminal 301, a supply tank 303 for directly supplying thinning agent to the nozzles 305, 306 for TEBR and BSR, and a pump 304 for drawing thinning agent from the supply tank 303 and supplying the thinning agent to the nozzles 305, 306 for TEBR and BSR.
The storage tank 302 and the supply tank 303 have scale marks by which one identifies the respective level of thinning agent as “L (low)” and “H (high)”. When the thinning agent in the storage tank 302 reaches the scale mark “L” of the storage tank 302, thinning agent is supplied from the input terminal 301 to the storage tank 302 until the level of agent reaches up to the “H” mark in the storage tank 302. When the thinning agent in the storage tank 303 reaches the “L” scale mark, thinning agent is supplied from the storage tank 302 to the supply tank 303 until the level of agent reaches up to the “H” mark. In other words, when the level of thinning agent in a respective tank 302, 303 falls to the “L” scale mark level, the respective tank 302, 303 receives additional thinning agent from its corresponding supply source until the tank 302, 303 is again filled to the “H” level.
The thinning agent drawn by the pump 304 is supplied from the tank 303 to the nozzles 305 and 306 for TEBR and BSR through a filter (which is not shown) for removing contaminants.
The thinning agent supplying system of the prior art, however, has certain problems. For example, bubbles are generated in the storage tank 302, the supply tank 303, and the supply pipe which may cause defects during the post-process, TEBR process.
Second, since the pump 304 is driven by N2 gas, fluid flow cannot be uniformly controlled. As a result, bubbles are generated at pump 304 when the pump 304 is driven.
Third, when the thinning agent reaches the “L” scale mark of the supply tank 303, thinning agent is supplied from the storage tank 302. However, the thinning agent in the storage tank 302 may reach the “L” scale mark before the supply tank 303 is refilled. In other words, the storage tank 302 is not always ready to supply thinning agent, which may interrupt smooth supply of the thinning agent.
Fourth, since the thinning agent is supplied from the input terminal 301 to the pump 304 through the storage tank 302 and supply tank 303, there are many places along the supply chain where a problem may occur. As a result, the equipment is subject to frequent breakdowns.